Radio Resource Allocation

It is important to differentiate physical and logical channels. A physical channel is
denoted as a packet data channel (PDCH), taken from a common pool from the cell.
Allocation can be driven by traffic load, priority, and multislot class (see Table 12.4).
Logical channels are divided into traffic and signaling (control) channels. One handset
can use several PDTCH (data traffic) channels. A packet broadcast channel PBCH
supports point-to-multipoint services and carries information on available circuitswitched
bearers.
A handset-originated packet transfer can be done in one or two steps. The two-step
process involves a resource request and then a channel assignment (logical channel
request followed by physical channel assignment) or both steps can be done at once.
On the downlink (base to handset), the handset is paged, the mobile requests a physical
channel, and the packet is sent.
A physical data channel has a multiframe structure of 52 frames, which is 240 ms
long. Note that a 26-frame multiframe (120 ms) is identical to an IMT2000DS multiframe
(12 × 10 ms frames).
As the offered traffic is moved into the network, it is controlled by the data link and
transport link layer protocols. GPRS tunneling protocol (GTP) is used to transfer data
packets over the transmission plane managed by the GTP tunnel control and management
protocol (using the signaling plane) to create, modify, or delete tunnels. UDP is
used for access to IP-based packet data networks, which do not expect reliability in the
network layer or below. IP is employed in the network layer to route packets through
the backbone. All of the packets are carried by the ATM transport layer. 295